Polycarbonates derived from reactions involving organic dihydroxy compounds and carbonic acid derivatives have found extensive commercial application because of their excellent mechanical and physical properties. These thermoplastic polymers are particularly suited for the manufacture of molded articles where impact strength, rigidity, toughness, thermal and dimensional stability as well as excellent electrical properties are required.
Although polycarbonates have some inherent flame resistance being self-extinguishing (V-2 at 1/8" thickness according to UL Subject 94), ever more demanding applications have required improved flame retardance.
Furthermore, it has been found that articles molded from conventional polycarbonates tend to exhibit both low heat deflection and Vicat softening temperature (ASTM D-648-72 and ASTM D-1525-76, respectively).
U.S. Pat. No. 3,269,986 relates to aromatic polycarbonates, the structure of which is characterized by alternating carbonate groups and sulfone-containing organic groups.
In accordance with the present invention, a copolycarbonate is provided having improved flame retardance, mechanical properties at elevated temperature and good physical properties.